1. Field of the Invention
The present invention relates generally to the field of electrical power transmission and distribution systems and more particularly to method and apparatus for determining protective device operations and locating fault conditions via the monitoring and detection of system conditions obtained from sensed circuit parameters.
2. Description of the Related Art
In electrical power distribution systems, various customers and users are supplied with electricity in networks such that power may be provided to the users from more than one system network path or more than one source. In this manner, faults may be isolated via sectionalizing while maintaining power delivery to the users who are not in the immediate vicinity of the faulted section; i.e., where the fault occurs. To achieve this purpose, a variety of devices are arranged throughout the distribution system at appropriate locations to efficiently provide for the interruption and isolation of faults. These devices include fuses, circuit breakers, reclosers, sectionalizers, and remotely and locally operated distribution switches.
The circuit breakers are located near the sources of the supply to the distribution system. Additionally, reclosers are located farther (downstream) from the points of supply at the breakers. Breakers and reclosers include the sequenced operation of reclosing cycles in the presence of overcurrents whereby the delivery of electric power is interrupted via the opening of the circuit for predetermined intervals followed by the closing of the circuit. Hereafter, breakers and reclosers are utilized interchangeably. The reclosing sequence continues until either the fault is cleared or a predetermined number of reclosing operations have taken place (e.g. , four) whereupon the recloser locks out to continuously open the circuit until appropriate action can be taken by maintenance personnel to repair the circuit. In this manner, momentarily occurring overcurrents or fault conditions which are self-clearing allow the restoration and maintenance of power delivery to the system without permanent opening (lock out) of the circuit.
Farther downstream from the source of supplies of the network, sectionalizers may be provided which are arranged to count the number of recloser operations. After a particular number of counts, for example three where the recloser has a total of four sequences of operation, the sectionalizer will open during the recloser open time so as to isolate a particular fault and allow the recloser to successfully reclose. At other locations, such as in branch sections or feeder lines, fuses may be provided which are coordinated with the other protective devices to sense overcurrents and faults so as to interrupt current before the operation of the circuit breaker, reclosers, and/or sectionalizers. Additionally, distribution switches capable of remote or local operation are provided at various points along the network to provide suitable isolation, sectionalizing, and re-routing of power via different sources.
Information about system operation and control of the system can be provided from each distribution switch or circuit point to a master station via suitable communication channels--radio, fiber-optics, land lines, or power-line carrier. For example, information can be obtained corresponding to the lockout condition of particular breakers as well as the voltage and current at particular points in the network. Additionally, fault indicators can be provided at suitable points to report as to the location of the fault on the network. Control of the system is available via the remote operation of sectionalizing devices equipped with remote terminal units (RTU's).
While particular information about parameters at the remote locations is available to a master station, the lockout condition in some systems is not readily discernable, and the determination of upstream protective device operations and the location of faults is only generally ascertainable at the master station. Additionally, presently available methods can erroneously respond as a result of magnetizing inrush currents, cold-load pickup, and backfeed conditions. Thus, the location of a fault is not confidently known via the information received at the master station. Accordingly, the remote terminal units and the distribution switches along the network cannot be utilized to efficiently locate, isolate, and restore the system after the occurrence of a fault or overcurrent condition.